Background: Enterococci are nosocomial pathogen. Their pathogenic potential has been attributed to their ability to resist antimicrobial drugs intrinsically, acquire and distribute antibiotic resistance determinants and adapt to changing environments. Linezolid resistance occurs by the mutations in the domain V of 23S rRNA, the presence of the cfr gene or mutations in the L3 and L4 ribosomal proteins. Erythromycin resistance is mainly due to target-site modification by the rRNAmethylating enzyme encoded by the erm gene or mediated by efflux pump mechanisms. This study aimed to detect and characterize the antimicrobial resistance mechanism to oxazolidinone (linezolid) and macrolide (erythromycin) among clinical isolates of Enterococci. Studies describing theresistance to erythromycin and linezolid are limited.

Objective: This study aimed to detect and characterize the antimicrobial resistance mechanismto oxazolidinone (linezolid) and macrolide (erythromycin) among clinical isolates of Enterococci.

Materials and Methods: A total number of 150 clinical isolates were included in this study. Susceptibility to various antibiotics was determined by disc diffusion. Minimum Inhibitory Concentration (MIC) was ascertained by agar dilution method for linezolid and erythromycin. Polymerase chain reaction was done to detect the genes, ermB and cfr that encode for erythromycin and linezolid respectively.

Results: Among 150 isolates, predominant were Enterococcus faecalis 116 (77%)  followed by  Enterococcus faecium 34 (23%). Of the 150 study isolates, the susceptibility to ampicillin was 64.6% (97/150), high level gentamicin 47% (70/150), linezolid (100%) and vancomycin (100%). Of the 90 exudative enterococcal isolates, only 13 were susceptible to erythromycin. Of the 77 erythromycin resistant isolates, ermB gene was detected in 42 and exhibited a high levelresistance with >32 mg/ml. The gene encoding for linezolid resistance, cfr was not detected in any of the study isolates.

Conclusion: High level resistance to erythromycin is mediated by ermB. Vancomycin and linezolid resistance were not encountered in the study. However, continuous monitoring of antimicrobial resistance of Enterococcus species is necessary to provide a guide for the appropriate selection of antibiotics for treatment and to implement preventive measures.